We've installed a Paws-I-Trip pan system and night latch dog. Pan tension after waxing the trap on the two coiled version runs an average of 2.1 pounds which we have found to be a very good number for a multi species trap. This trap is fast and excellent results were obtained using it two coiled. We do not recommend using the 4-coiled version if grey fox is your target animal. The 550 is an excellent live market trap as well as the trap to use on a mixed species line. Small enough for fox and tough enough for the nastiest coyote.
If you are not planning on 4-coiling your MB-550-RC's we strongly recommend cutting the excess spring pins off leaving 1/2" protruding from the frame. We personally (along with many of our customers who have used the 550) prefer underalls to pan covers for this trap. The underalls increase the pan tension slightly resulting in full pad or foot catches and the number of snapped traps is reduced to near zero. We have obtained excellent results on grey fox with the 2-coiled 550 and underalls.